A very important part of Aztec religion was human sacrifice. They beleived that the gods needed human sacrifice to survive and people needed the gods to survive. They believed that the heart was the best gift that they could offer so they normaly sacrificed people by ripping out their heart with a knife. They decided who would be sacrificed using a game called ulama. It was played using a rubber ball that was hit through a stone hoop. The winners were greatly celebrated and the losers were sacrificed.